Worm and worm-wheel transmissions



G. NIEMANN worin AND wom-wmzm TRANSMISSIONS -Filed Aug. so. 1966 Gusfa.v Niemann INVENTO Holte Holte AT'I'ORNEYS United States Patent O 3 396,595 WORM AND WORNf-WHEEL TRANSMISSIONS Gustav Niemann, 39 Flemingstrasse, 8 Munich 27, Germany Filed Aug. 30, 1966, Sex. N0. 576,065 Claims priority, application Germany, Aug. 31, 1965, N 27,271 7 Claims. (C1. 74-425) ABSTRACT OF THE DISCLOSURE A worm and worm-wheel transmission. The transm'ission includes a rot-ary worm means and a rotary wormwheel means coacting therewith, the wenn mea:ns being made of hardened steel while the wonnwheel means is made of cast iron which initially is provided at its teebh with a relatively thin, scuff-preventing surface layer of a material softer than the material of the worm-wheel means. During running in of the wenn and worm-wheel means, the relatively thin scufl-preventing surtfiace layea 0f material which is softer than the material of t1he wormwheel means becomes worn away at the load-1zransm-itting surface portions of be teeth so that at thdse latter portions the hardened steel coacts directly with the cast iron of the wonn-wheel means, whiah, because of this running in, has an exceedingly smooth snrface coacting in a highly efiicient manner with the wenn means. This oast iron wormwheel means has great resistance to wea.r and pitting and great strength, far beyond conventional bronze wheels, =so that the 10ad transmitting capacity of the transmission of ehe invention is greater (h-an that of a comparable size where the wonn-wheel is made of bronze. Of course, the relatiw:ly thin soft coating men1ains at the non-load carrying -p0rtions 0f the teeth of nhe wormwheel.

The present invention relates to trans-mssions.

In parfiicular, the present invention =relates to wormand-wornrwheel transmissions where a womm, which may be tapered or which may be of constant diameter, coacts with a wonnwheel for the purpose 0f transmitting relatively 1arge loads.

With comventional worm-and-wonn-wheel transmissions designed for the transrnission 0f 1arge loads, 'vhe wonn is made of hardened stee1 and has ground tooth surfaces, and a worm-wheel of bronze coacts with this worm, because such a pair of transmitting elements has been found to have the greatest load-transmitting capability. Thema an'e known transmissions of this type where the wenn is made of hardened steel and has ground tooth surfaces, While the wonn-wheel is m ade of cast iron, and such a transmission presents the advantage of being le!ss expensive than a transmission where Ehe wonn-wheel is made 0f bronze. However, the greate;r strength of the C3St iron renders the running-in of the transrnission more dif ficult to carry out, which is to say the adapting of be tooth surfaces of the worm-wheel to the tooth sumfaces of the wenn. Moreover, the greater strength of the oast iron used for the wonnwheel easily results in soratching and roughening or even scuffing of the t0Oflh surfaces of the worm, and therefore the eificiency of tne transmission &s xreduced and visible danmaging 0f the transmission is apparent. As a result, worm-and-worm-wheel transrnissions which include a worm-wheel made of cast iron have an extremely 10W load-transmitting capability and a 10W efi'iciency, as compared to a t1'an-smissi0n w here the wormwhee1 is made of bronze. Thus, finansmissions where a wenn of iha;rdsn&d stee1 coacts with a worm-wheel of cast iron are used only for transrnissions which are loaded to a small extent and/or are operated with relatively slow speeds 0f sliding movement between their tooth surface1s.

It is a primary object 0f the present invention to prov'ide a worm-and-wonn-wheel transmission capable of transmitting la=rge loads and having an even greater loadtransmitting capaoity than a transmission where the wenn i's made 0f hardened stee1 and the wonn-wheel is made of bronze, so that larger load oan be transmitted with ehe transmission of t1he present inventon than with conventional transmissions of the same size.

The invention is illustrated by way 0f example in the accompanying drawing which fonns pa-rt of (bis -application and in which a transrnissi0n according to the present invention i s fragmentarily illustmated in a partly sectional view with the plane of the section taken normal to the axis of the warm-wheel. 7

Referring now to the drawing, it will be seen that 1ihe transmiss ion 10 of the present inventon, which is illustrated therein, includes a rotary wonn means 12 made of hardened stee1 and having ground tooflh snrfaces. T hi s warm means 12 coacts With1a worm-wheel me2ms 14 made of cast iron, and in aocordance With the prsent invention the tooth surfaces of the worm-wlheel means 14 have been provided with a mel-atively thin damage-prevent'hg surface layer 16 being softer than the material of which the worm-wheel means 14 is made, so th=at the material of the surface layer 16 is in fact softer than cast iron, in t-he illusflrated exarnple.

The surface Iayer 16 can be provided on 11115 wormwheel means 14 by phos;phate treatment as well as by admium-pklting, by tinning, or by coppexr-plating, so th at the material of the surface layer 16 will be phosphates, cadmium, tin, or copper. However, the invention is not limited t0 these specific swrface laye11s, since it is only reqnired that the material of the surface layer 16 be softer than that 0f the wonn-Wheel 14 so as to prevent darnaging or scufling of the ground surface of the hardened steel wenn 12 during running in, as pointed out above.

A transmission according to the present invention will run in just as fast and just as reliably, u-p to transmission of its rated load, as a tnansmission where the wonn-wheel is made of bronze. Furthennore, with1respe'ct to efiiciency 01' loss of output, the transmission of the invention is practica1ly of Ehe same high quality as a uransmislsion Where the worm-wheel is made of bronze. Because 0f Uhe greater resiistance to wear and pitting of a wonn-wheel made of Gast iron and because 0f the greater strength of the oast iron, it is possible to achieve with the transmission of the invention, however, a substantially greater load-transmission, at the load-oarrying surfaces where the thin coating has worn away during mnning in, than is possible Wiflh a transmission of comparable size where t1he wennwheel is made 0f bronze.

By providing in cooperation with a wenn made of hardened istee1 a wonn-wheel made of cast iron, the combination 0f the present invention :achieves at Ihe loadcarrying tooth surfaces of steel and cast iron of the ransmission load-transmitting capacities which up to the present time have been unknown in high-power wormand-wonn-wheel t:ransmissions. Moreover, a transmission according to flhe present invenc-ion s more insensitive to overloads than a trannnission of compsurable size where the worm-wheel is made of bronze. F0r the relatively short periods of time, the tnansmission of the invention can be overloaded up to 250%, without, as has been known to happen with bronze wann-Wheels, defonnafiion of tne teeth of the worm-wheel with msulting damaging of the transmission. In addition, the high-power wann-andworm-wheel transmi ssi0n according to the present invention exhibits, aus compared t0 a conventional high-power transmission which includes a bronze wo nn-w heel, a far smaller sliding wear resulting frorn slippage between the tooth surfaces.

In addition to all of these advantages, the matexrial and manu=facturing costs for a transmission where the wennwheel is made of 'C2LSt iron is but a fraction f t'he material and manufactmring costs 0f a transrnission where the worm-Wheel is made of bronze.

The best operating conditions axre achieved With the transmission of fihe invention, as i's known per se for 0ther high-power transmissions, where a lubricant is used in the transmission which includes a scufiing-preventing additive. Thus, in a transmission of the present invention it i s prefenred to use Fa lubricant having as additive one 0u more chlor0-, phosphor-, leador sulfur-cornpounds, so that the lubnicant which forms part of the transmission of the invention Will render even more reliable the prevention of scuffing 0f the wurm.

It is 0f particula.r interest to apply nhe invention on a trainsmission Where the wenn has concave load-transmitting surfaoes, as indicated in the drawing, 'si-nce with Such surfaces the Hertzian pressure and also the tendency 0f scufi1ng of the tooth surfaces of the trans'mission, in the pairing of cast iron and steel, a1e at a minimurn. There- Lfore, the application of the features of the present invention to the con'shruction of transmissions 0f this latter type provides the greatest possible increase in load-transmitting capacity 18;1I1d efliciency.

What is cla irned is:

1. A transmssion compn'sing rotary wenn mean-s and rotary worm-wheel means coacting With said rotary wenn mea'ms, said worm means -and said wonm-wheel means being respectively made 0f materials which are prone to cause damage o1 scufiing of said worm means by sazid Worm-Wheel means, and said worm-wheel means havin g tooth swrfaces directly coacting with said wenn means, said tooth surfaces of said worm-wheel means having at non-loading carrying portions a relatively thin, scuflingpreventing surface layer of a material softer than said material of said Worm-wheel means and thin enough to be worn away du.ring runnin-g in so that the 1oad is transmitted between load-cazrrying surface portions where the material 0f said worm-wheel means is exposed through s'aid surface layer of softer matcrial for drect engagement with said worm means.

2. A transrnission as rec'ited in c1aim 1 and wherein said wenn mea-rrs is made of harde'ned steel a.nd has ground surfaces With which said worm-wheel means coacts, said worm-wheel means being made of oast iron, and saiid surface layer consisting of a material softem than cast iron.

3. A tman'smission as recited in claim 2 and wherein said non-load-carrying portions of Lsaid tooth-sunfaces o f said woum-vvheel means am: cadmium-plated to be provided with said surface layer.

4. A transmfission 'as recited in claim 2- and wherein seid non-load-carrying portions of said tooth surfaces of said worm-wheel means are coated with (in (tinned) to be provided with said surface 1ayer.

5. A tra11smission as recited in laim 2 a.nd Whe rein said non-load-carrying portions of said tooth surfaces of said worm-wheel means are copper-plated to be provided with said surface layer.

6. A transmission as -recited in claim 1 -and Wherein a lubricant coacts with said wenn means and worm-wheel means, said lubricant includ=ing a scufiing preventing additive.

7. A tramsmission as redited in claim 1 and wherein said warm means t1as concave tooth surfaces t:oacting W-ith said wormwheel means.

References Cited UNITED STATES PATENTS 1316,270 9/1919 Calkins 74460 1,393,886 10/1921 Doty 74-460 2, 183,667 12/ 1939 Buckendale. 2266377 12/1941 Neely et a1.

FOREIGN PATENTS 440,786 1/ 1936 Great Britain. 715,462 9/1954 Great Britain.

FRED C. MATTERN, JR. Primary Examiner.

LEONARD H. GERIN, Assistant Examz'ner. 

